1. Field of the Inventions
The present inventions relate to steering systems for watercraft, and more particularly, to such systems that electrically connect a steering device with an outboard motor to each other.
2. Description of the Related Art
Japanese Patent Document JP-B-2959044 describes a steering system in which an outboard motor, functioning as a watercraft propulsion unit having an internal combustion engine, a propeller (screw) mounted to a lower unit, etc. is disposed outside of a watercraft hull. A steering motor, which functions as a steering actuator for steering the outboard motor in the right and left directions, is provided in a coupling portion between the watercraft hull and the outboard motor. The steering motor and a steering wheel are connected to each other via a signal cable through which signals can be transmitted and received. The steering wheel has a rotational angle sensor. The steering motor rotates based upon a rotational direction and a rotational angle of the steering wheel detected by the rotational angle sensor to thereby steer the outboard motor.
FIG. 10 is a schematic illustration showing known relationships between steered angles of a conventional outboard motors and torques necessary for steering operations. In FIG. 10, the horizontal axis indicates steering angles (“0” represents a steering angle 0°, and the right side range relative to the position of “0” represents right directional steering angles, while the left side range relative to the position of “0” represents left directional steering angles), and the vertical axis represents magnitudes of the torque necessary for the steering operations (it is depicted that the higher the location is in FIG. 10 the larger the torque is when the outboard motor is steered rightward, and it is depicted that the lower the location is in FIG. 10 the larger the torque is when the outboard motor is steered leftward). Also, regarding the torque necessary to steer, the higher the location (the first quadrant) is in FIG. 10 the larger the torque when steered rightward (the right side range relative to the vertical axis), and it is also depicted that the lower the location (the third quadrant) is in FIG. 10 the larger the torque is when steered leftward (the left side range relative to the vertical axis). On the other hand, regarding the torque necessary to steer back, it is depicted that the lower the location (the fourth quadrant) is in FIG. 10 the larger the torque is when steered back from the right direction (the right side range relative to the vertical axis), and it is also depicted that the higher the location (the second quadrant) is in FIG. 10 the larger the torque is when steered back from the left direction (the left side range relative to the vertical axis).
As shown in FIG. 10, when the outboard motor is steered rightward from the steered angle 0° (in the situation indicated by the arrow (1) of FIG. 10) and also when the outboard motor is steered leftward from the steered angle 0° (in the situation indicated by the arrow (3) of FIG. 10), the necessary torque is the maximum at the steered angle 0°, and the larger the steered angle the smaller the necessary torque. On the other hand, when the outboard motor is steered back in the direction toward the steered angle 0° under a condition that the outboard motor has been rightward steered (in the situation indicated by the arrow (2) of FIG. 10) and also when the outboard motor is steered back in the direction toward the steered angle 0° under a condition that the outboard motor has been leftward steered (in the situation indicated by the arrow (4) of FIG. 10), the larger the steered angle the larger the necessary torque, and the smaller the steered angle the smaller the necessary torque.